1. Field of the Invention
This invention generally concerns a universal battery operated measuring device for vehicular diagnostics which offers a number of diagnostic options in particular due to the universal use of various internal and external sensors and their link-up to one another.
2. Discussion of Related Art
Chassis dynamometers, such as those described in European Patent 433,668, are often used to determine the minimum braking deceleration stipulated by law. However, this device can be used only with standard vehicles. Special vehicles are tested mainly by driving tests, however.
Use of traditional braking deceleration measuring devices with a spring-mass system has the disadvantage that they also measure acceleration due to gravity to some extent. This occurs due to the fact that the center of gravity of the vehicle body is above the point where the forces act (contact: tires with road surface). Therefore, the front shock absorbers of the vehicle are compressed in braking deceleration while at the same time the rear shock absorbers are elongated. As a result, the angle of the vehicle with respect to the road surface changes, that is, it pitches forward. This pitch angle xcfx86 produces a component attributable to acceleration due to gravity which has nothing to do with the actual deceleration of the vehicle. The acceleration due to gravity component is calculated from gxc2x7sin(xcfx86).
On the other hand, this angle causes a reduced sensitivity to the actual acceleration, so the measured deceleration is calculated from the actual deceleration multiplied by cos(xcfx86).
In the past, a so-called gyro-stabilized platform has been used to overcome this problem for accurate measurements, and the measuring devices have been mounted on this platform. This platform holds the sensors in a horizontal position with respect to all pitching and rolling motions longitudinal and transverse) of the vehicle body during the test run of the vehicle. Therefore, the errors described above do not occur. It is obvious that such a platform is an expensive device that is not easy to handle.
Another method is to xe2x80x9cshootxe2x80x9d shots of color onto the ground at intervals by using a special device. For example, an ink cartridge may be ignited every second in such a device. An actual deceleration can be calculated on the basis of the distances measured manually after the braking test.
One object of this invention is to create a measuring device for motor vehicles that will permit an accurate and inexpensive method of detecting the deceleration and acceleration of a vehicle, determining engine power and evaluating shock absorbers.
According to this invention, the longitudinal and/or transverse acceleration which is subject to error is measured via a sensor, and the corresponding influences of acceleration due to gravity are corrected by means of a separate angle sensor, likewise separated according to longitudinal and transverse directions. To do so, an angle sensor may be mounted in the device in such a way that the sensitive direction corresponds to the pitch angle (for the longitudinal acceleration) or the pitching or rolling angle for transverse acceleration. The respective signals for the longitudinal and transverse acceleration can be compensated as illustrated in FIG. 5.
In tests in decelerating from a high speed with relatively low deceleration values, substantial braking distances and times are obtained in some cases. Since inexpensive angle sensors (not fully cardanic) indicate only a change in angle, this angle change must be integrated to obtain the angle xcfx86. Therefore, minor offset errors with the sensor can result in a considerable angle error after integration. Therefore, the offset error can be compensated according to this invention.
The braking test can be stored online in a memory in the device. After the measurement, a starting or stopping point (beginning/end) can be defined. Then the zero point of the angle sensor can be set so that the angle integral (all angles in the entire measurement time) is zero. In addition, with utility vehicles which have a tachograph, the path signal of the tachograph is entered via an amplifier input and processed. This path signal can be offset with the adjustment factor (k factor) of the tachograph. This calculation yields a standardized path signal (for example, one meter of distance traveled corresponds to eight pulses).
The distance can be converted by a first differentiation into a corresponding traveling speed. The acceleration signal can be obtained by differentiating the speed once again.
Furthermore, it is possible to obtain a standardized signal (for example, eight pulses per meter) for different types of tachographs. This eliminates the correction in the device as described above.
Due to the relatively high resolution of the path sensor, the time resolution of the acceleration is not particularly great, especially at low traveling speeds. Therefore, it is proposed according to this invention that the built-in acceleration sensor be adjusted with the tachograph signal at higher traveling speeds.
Thus, a corrected deceleration and acceleration signal can be obtained by means of the sensors present in the device and the methods described above. Velocity is obtained by integrating the acceleration signal thus derived.
In addition, engine power can be determined with the portable measuring device according to this invention. The vehicle mass can be input into the device for this purpose. Then the acceleration can be determined in a driving test, and the velocity can be obtained by integrating the acceleration. The tractive power of the vehicle can be calculated according to Newton""s second law, F=mxc2x7a, where an acceleration power P-Rad [wheel power]=Fxc2x7v can be determined by multiplication by velocity.
After reaching the maximum engine rpm, the drive can be separated by a clutch. The driving resistances then brake the vehicle mass. Again, a deceleration force (F=mxc2x7a) can be obtained from the deceleration occurring here multiplied by the vehicle mass, and a deceleration power (P-Ver [power loss]=Fxc2x7v) (or a so-called power loss) can be calculated by multiplying by the integrated deceleration (speed). Then the acceleration power and the deceleration power (or the power loss) can be added geometrically, yielding a total power or engine power. Since the engine is coupled during acceleration and is decoupled in deceleration, a mass component of the engine corresponding to a centrifugal mass is added to the vehicle mass during the acceleration phase to compensate for the absence of the centrifugal mass of the engine in the decoupled state. It should be pointed out that either the mass component for the acceleration phase or the mass component for the deceleration phase can be corrected. Thus, according to this invention, no rolling set with corresponding centrifugal masses are needed to determine the engine power.
In addition, the so-called pitching or rolling angles can also be measured by means of the built-in sensors according to this invention. In addition, the wheel base can also be input as additional data, for example, by a keyboard. If the vehicle is set in vibration, the damping can be calculated directly, and the measuring device need be located only on a flat surface in the passenger compartment.
In addition, it is possible to implement an evaluation of the shock absorbers directly during the braking test. The pitch of the vehicle is greater the greater the braking deceleration. Therefore, a quantity is calculated which is modified by the deceleration, that is, the pitch angle is measured per m/s2 of deceleration. Thus, according to this invention the shock absorbers of a vehicle can be tested and evaluated without any great mechanical outlay.